Type designated in Setchell, W.A. & Gardner, N.L. (1933). A preliminary survey of Gigartina, with special reference to its Pacific North American species. University of California Publications in Botany 17: 255-339, Plates 46-65.

Description: Gametophytes reach 20 cm in length and are erect from basal discs. Thalli are broadly to narrowly and fairly regularly dichotomous, with or without marginal and surface proliferations, and with the main axes usually conspicuously channeled. Cystocarps lack an enveloping filamentous hull round the carposporophyte. Tetrasporangia occur singly and intercalarily within erect filaments.

Information contributed by: G.T. Kraft.
The most recent alteration to this page was made on 23 Jan 2017 by M.D. Guiry.

Characters considered diagnostic of Mastocarpus:

Kim (1976) distinguished gametophytes of Mastocarpus from those of Gigartina by the absence of a filamentous hull around the carposporophyte (comparable to the situation in Chondrus), the presence of sterile laterals on the basal cell of the carpogonial branch, and the smaller number of gonimoblast initials, which are not exclusively directed inwardly. Guiry et al. (1984) emphasize the channelled thalli, carpogonial/cystocarpic papillae, and the unchained tetrasporangia in heteromorphic tetrasporophytes as distinghishing features of the family and genus.

Comments: The type species occurs in the north Atlantic Ocean from Russia to Portugal and from Morocco to Mauritania in the east and from Rhode Island to Newfoundland in the west. Two other species are common in the eastern Pacific from Alaska to Baja, and a fourth is known from the northern Pacific from Hokkaido to south-eastern Alaska. Both the gametophyte and tetrasporophytic stages are characteristic of high to mid intertidal rocks on open coasts, although the type species also occurs subtidally (Dixon and Irvine, 1977). Until Kim's (1976) study of the Gigartinaceae, Mastocarpus had been treated as a subgenus of Gigartina. Kim informally proposed the family Mastocarpaceae for the assemblage, although Denizot (1968) had earlier established the Petrocelidaceae for "species" the tetrasporophytic stage. Fletcher and Irvine (1982) described gametophytes and an isomorphic alternation of generations in Petrocelis hennedyi, a species of very similar vegetative anatomy to P. cruenta but with catenate intercalary tetrasporangia. This taxon was later transferred to the genus Haemescharia of the Haemeschariaceae by Wilce and Maggs (1989).

A monotypic family of 4-6 species of cool- to cold temperate Northern Hemisphere distribution. Gametophytic plants are erect from discoid bases and are composed of a filamentous medulla of extensively secondarily pit-connected cells surrounded by a broad cortex of pseudodi-/trichotomous filaments oriented perpendicularly to the medulla. Female gametophytes are procarpic, the carpogonial branches being 3 celled and generally bearing one or two sterile lateral cells on the basal cell. The supporting cell becomes the generative auxiliary cell following fertilization, and multiple gonimoblast initials grow as filaments directed both inwardly and outwardly, with most development taking place thallus inwardly. Carpogonial branches and cystocarps are formed in papillar outgrowths, the cystocarps consisting of pockets of catenate carposporangia isolated among sterile placental filaments of mixed and partially fused carposporophyte and gametophyte cells. Tetrasporophytes are heteromorphic to gametophytes, being non-calcified crusts anchored without rhizoids to rock and consisting of a several-layered hypothallus that gives rise to perpendicular, erect, simple to sparingly branched dorsal perithallial filaments occasionally linked by secondary pit connections. Tetrasporangia are cruciate and intercalary in a deeply buried layer of the perithallus.

Several studies, beginning with that of West (1972) and continuing with West et al. (1977, 1978, 1983), Dion (1979), Masuda and Kurogi (1981), Guiry and West (1983), and Masuda et al. 1984, 1987), have shown that certain common species of what were previously considered Gigartina from Europe, North America and Japan in which tetrasporophytes were formerly unknown alternate with a crustose tetrasporophytic phase identical to described species of the genus Petrocelis. In some isolates, a direct type of life history has been demonstrated, the basal discs from which erect thalli arise directly yielding lambda carrageenan indicative of diploidy, and the erect fronds producing kappa carrageenan, which normally typifies gametophytes in this family and the Gigartinaceae (West et al. 1983).

Numbers of names and species: There are 29 species names in the database at present, of which 15 have been flagged as accepted taxonomically on the basis of the listed literature under the species name. In some instances, opinions on taxonomic validity differ from author to author and users are encouraged to form their own opinion. AlgaeBase is a work in progress and should not be regarded as a definitive source only as a guide to the literature..

Names: ('C' indicates a name that is accepted taxonomically; 'S' a homotypic or heterotypic synonym; 'U' indicates a name of uncertain taxonomic status, but which has been subjected to some verification nomenclaturally; 'P' indicates a preliminary AlgaeBase entry that has not been subjected to any kind of verification. For more information on a species click on it to activate a link to the Species database):

Setchell, W.A. & Gardner, N.L. (1933). A preliminary survey of Gigartina, with special reference to its Pacific North American species. University of California Publications in Botany 17: 255-339, Plates 46-65.

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Contributors
Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera,
organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA)
and intended to be published in CD format.
These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above.
The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.